However, ultrasound determination of the date of ovulation has the same imprecision as does the ultrasound estimate of the gestational age and, therefore, a precise date of conception cannot usually be determined as with in vitro fertilization. In addition, although a woman is most likely to become pregnant if she has sex on the day of ovulation conception may also occur from live sperm still in her reproductive tract on the day of ovulation if she had sex for up to five days before ovulation [26,27]. even though they said my baby was 6 days ahead my conception date doesnt change? The date of my last period was November 28th which would make me 25 weeks 4 days."Ultrasound measurement of the embryo or fetus in the first trimester (up to and including 13 6/7 weeks of gestation) is the most accurate method to establish or confirm gestational age" [24]. When people discuss how far along in pregnancy someone is, they tend to do so in general terms: “She’s in the first trimester” or “She’s four months along.” However, many people have only a vague idea of what those phrases really mean.I know when they use your period they say that the baby wasn't actually conceived until about the 14th day. But I was wondering, when they did my date scan at 8 weeks they said my due date would actually be September 8th.

In cases where the date of conception is known precisely, such as with in vitro fertilization, the EDD is calculated by adding 266 days to the date of conception. American College of Obstetricians and Gynecologists.

Determining the Estimated Due Date The estimated due date (EDD or EDC) is the date that spontaneous onset of labor is expected to occur. Conceptional age, menstrual age, and ultrasound age: a second-trimester comparison of pregnancies of known conception date with pregnancies dated from the last menstrual period.

The due date may be estimated by adding 280 days ( 9 months and 7 days) to the first day of the last menstrual period (LMP). The accuracy of the EDD derived by this method depends on accurate recall by the mother, assumes regular 28 day cycles, and that ovulation and conception occurs on day 14 of the cycle.

Examples include if you have irregular menstrual cycles or long menstrual cycles, or if you became pregnant directly after a miscarriage or after extended breastfeeding without menstruating.

“Exercise extreme caution with regard to last menstrual period (LMP) on history taking.

The accuracy of h CG measurement in determining the week since conception was more than 93%.